A femtocell refers to a subminiature home base station connected with a mobile communication service provider network through an IP by using a wired Internet (xDSL/Cable) line as a base station line, and corresponds to a cell for providing voice and data services to 4-8 users. A first advantage of the femtocell allows a radio quality within the home to be improved, stably provide the data service, and reduce loads of a macro cell by absorbing voice and data traffic generated at home since the femtocell is a type which has a dedicated base station installed in every home. Accordingly, it is possible to increase the base station line and reduce a maintenance cost by utilizing a wired infra within the home widely distributed. As a second advantage, it is possible to provide a new fixed mobile substitution (FMS) solution corresponding to a fixed mobile convergence (FMC) based on a wired service provider. That is, there is no limitation in a terminal unlike an FMC service in a dual mode due to the use of a mobile communication frequency, and there is no effect on the macro cell even through a use amount within the home is increased unlike a conventional FMS scheme.
However, the femtocell has a technical problem to solve an interference problem caused between the macro cell and the femtocell as well as including the above mentioned advantages. FIG. 1 is a view for describing an interference phenomenon generated between the macro cell and the femtocell.
As illustrated in FIG. 1, two areas are defined within the femtocell, the two areas corresponding to a femtocell coverage area in which a pilot signal intensity of the femtocell is larger than a pilot signal intensity of the macro cell and a macro cell dead zone in which the pilot signal intensity of the femtocell is larger than the pilot signal intensity of the macro cell by a predetermined value or more (for example, 4 dB in a WCDMA).
A terminal cannot access the macro cell in the macro cell dead zone. Since the pilot signal intensity of the macro cell becomes smaller as it is closer to a cell boundary area of the macro cell, a size of the dead zone becomes larger. A terminal located in the boundary area of the macro cell transmits a radio wave with very high power in order to access the macro cell, but the radio wave causes interference with the femtocell. This interference corresponds to interference due to an uplink. That is, large mutual interference between the macro cell and the femtocell is generated in the femtocell located in the boundary area of the macro cell, so that a phone communication quality is deteriorated.
It is difficult to form a femtocell coverage in a cell center area of the macro cell since the signal intensity of the macro cell is very large. Accordingly, a service of the femtocell itself is very difficult.
The related art to solve such an interference problem proposes a method through a power control of the femtocell and a method of allocating a different frequency used in the femtocell from that of the macro cell. However, the power control method has a limitation in mitigating inter-cell interference because the power control method is limited to a static method, and the method of allocating only a different frequency to the femtocell has a problem of deteriorating frequency use efficiency and frequently generating a call disconnection phenomenon when a handover between the macro cell and the femtocell is performed.